1. Field of the Invention
The present invention relates to a lithographic apparatus and a device manufacturing method.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. The lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs), flat panel displays, and other devices involving fine structures. In a conventional lithographic apparatus, a patterning means, that is alternatively referred to as a mask or a reticle, can be used to generate a circuit pattern corresponding to an individual layer of the IC (or other device), and this pattern can be imaged onto a target portion (e.g., comprising part of one or several dies) on a substrate (e.g., a silicon wafer or glass plate) that has a layer of radiation sensitive material (e.g., resist). Instead of a mask, the patterning means can comprise an array of individually controllable elements that generate the circuit pattern.
In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include steppers, in that each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and scanners, in that each target portion is irradiated by scanning the pattern through the beam in a given direction (the “scanning” direction), while synchronously scanning the substrate parallel or anti-parallel to this direction.
Other possible modes of operation of lithographic apparatus are discussed below, including a pulse mode and a continuous scan mode applicable to apparatus including patterning means comprising an array of individually controllable elements, as mentioned above. With such apparatus, it is desirable to periodically update the array (often referred to as a spatial light modulator—SLM) to ensure that the instantaneous pattern generated is appropriate to the image to be transferred to the substrate. For instance, when operated in pulse mode (described below) the SLM can be updated as required between pulses of the radiation system. In a continuous scan mode rapid updating of the SLM can occur as the beam scans across the substrate.
The time required to update the SLM, i.e., load a new image frame on to the SLM, is a determining factor on apparatus throughput. For example, in the case of flat panel display (FPD) production, the apparatus can typically operate in a pulse scan mode with laser pulsing 50 KHz with 10/20 nsec pulse duration. Such a high frequency provides acceptable apparatus throughput, particularly because of the large substrate areas that are conventionally scanned to product FPDs. In order to load an SLM frame between pulses, in view of the large number of individually controllable elements, data transfer rates of the order of 10-100 Gpixels/sec or more are required. This can require the use of complex and expensive data handling and image driver systems. In addition, with such high data transfer rates, the chance of data errors occurring can be relatively high.
Therefore, what is needed is a system and method that reduces an amount of data required for maskless lithography.